How to make an progress bar for an NSURLConnection when downloading a file?

Question

I want to show up an progress bar while a download with NSURLConnection is happening. As I am getting data from the server, I could update the UI for every received package. But the problem is: How do I figure out how much data I have already, and how much data has to be downloaded? Probably in bytes... And then I have to do some math to get the percentage?

Answer 1

In your NSURLConnection delegate, implement something like this to find out the total content length. The server has to support this, but it will most likely work fine with static content:

- (void)connection: (NSURLConnection*) connection didReceiveResponse: (NSHTTPURLResponse*) response
{
    statusCode_ = [response statusCode];
    if (statusCode_ == 200) {
        download_.size = [response expectedContentLength];
    }
}

And then update progress like this:

- (void) connection: (NSURLConnection*) connection didReceiveData: (NSData*) data
{
    [data_ appendData: data];
    download_.progress = ((float) [data_ length] / (float) download_.size);
    // Broadcast a notification with the progress change, or call a delegate
}

In my case I have a download instance that has size and progress properties. They are owned by a global DownloadManager object that will take care of notifying interested parties of the download progress or state changes.